Preparation

Pulse 6 oz. chocolate wafers in a food processor until finely chopped. Transfer to a large bowl.

Pulse brown sugar, cocoa powder, malted milk powder, baking powder, kosher salt, and 2 cups flour in food processor several times to combine. Add butter and pulse until pieces are broken up into bits no larger than a pea. Add to bowl with chocolate and toss to combine.

Stir vanilla and 2/3 cup cream in a measuring glass to combine, then slowly drizzle over chocolate mixture, mixing with a fork all the while. Mixture will look dry once you’ve added all the cream. Knead dough a few times in the bowl (it will not come together and will look crumbly), then transfer to a large piece of plastic wrap. Bring the edges of plastic up and over dough and press down to incorporate floury parts, then wrap tightly. Use the heel of your hand to press down firmly on the dough, forcing it to tightly fill out the plastic. This will help the dough adhere into a single mass and help the flour hydrate. Chill dough until firm, at least 1 hour.

Preheat oven to 400°F. Roll out dough between 2 sheets of floured parchment paper to 3/4" thick (you might not have to roll it very much). Punch out rounds with cookie cutter as close together as possible. Transfer biscuits to a parchment-lined baking sheet and freeze 10 minutes.

Meanwhile, heat corn syrup, remaining 4 oz. chocolate, and remaining 1/2 cup cream in a heatproof bowl set over a saucepan of barely simmering water (bowl should not be touching the water), stirring often, until chocolate is melted
and mixture is completely smooth. Set bowl with frosting into a large bowl of ice water and let cool, stirring occasionally, until thickened but still pourable and shiny. Spoon a scant tablespoonful of frosting onto each biscuit; sprinkle with sea salt.

Do Ahead

Dough can be made 1 day ahead; keep chilled. Biscuits (without frosting) can be baked 2 days ahead; store airtight at room temperature.